1. Field of the Invention
The invention refers to an arrangement for starting a motor, especially in hand-held machines using a magnetic generator which induces alternating current dependent on the revolutions and thus charges an ignition charger element for ignition spark energy which serves the accumulation and provision of energy to generate an ignition spark. Moreover, the arrangements cover a trigger which scans the alternating current which is designed to activate an ignition circuit which is discharged with the primary coil of an ignition transfer interacting with an ignition charger element. The trigger has a circuit or other module to limit the revolution speed of the motor and this revolution limiter module works with a trigger charger element which is charged from a source of alternating current from the magnetic generator which can be discharged by at least one path for activating the ignition circuit. Further more, the invention refers to a revolution threshold regulator or toggle switch for same.
2. Description of the Related Art
As is known, an ignition spark is generated using an ignition module with which one revolution of the crankshaft of a machine is initiated. Hand-held tools with motors or combustion engines are already used, whose ignition is connected with a revolution governor in order to prevent too many revolutions as a result of failure or incorrect use. Too many revolutions can endanger the motor and the user. In order to limit the revolution speed of the motor, no ignition sparks are produced by the ignition device or ignition module above a preset revolution. The preset revolution upper limit is only slightly above the working revolution speed. This requires a precise revolution working limit with a narrow tolerance so that the ignition does not stop during normal operation.
However, current ignition modules with revolution limiters are relatively expensive. The accuracy of the revolution limits depends, on the one hand, on the accuracy of the parts used and their tolerances and, on the other hand, on the control and electricity supply of the energy for the revolution limiter circuit. This energy comes from the ignition spark generation. This problem has already been approached in patent publication WO 96/23 971 and U.S. Pat. No. 4,538,586. A substantial role in triggering the ignition process and thus also for the revolution limiter is the so-called ignition thyristor which ensures that the charged ignition capacitor connected to the ignition transformer or transfer is suddenly discharged. The ignition thyristor is not only used to trigger the ignition process but also to prevent the ignition trigger processes in order to limit the number of revolutions. This is managed by the energy for the ignition capacitor, which is induced by a charge coil, and is short circuited by the ignition thyristor so that the ignition capacitor is not charged.
We further refer to the current state of the technology in DE 196 45 466 A1, DE-AS 19 54 874, EP 0 584 618 A2 and U.S. Pat. No. 4,449,497.
DE-AS 19 54 874 has an ignition device for a motor where a switch with anode-cathode paths can be controlled in the conductive state when a maximum revolution speed is exceeded. In order to guarantee a defined switch through of the anode-cathode paths when the maximum admissible revolution is exceeded, the named publication suggests connecting a Zener diode to the control electrode of the ignition thyristor, whose anode is connected to the control cathode and whose cathode is connected to a monitoring capacitor. The effect of the Zener diode with the trigger capacitor, which provides energy for controlling the ignition thyristor, however, is not mentioned.
DE 196 45 466 A1 includes an ignition circuit for a motor with trigger coil and trigger capacitor which is charged therefrom. The control connection of an ignition thyristor to discharge the ignition capacitor charged from one of the ignition coils is controlled via a potentiometer-type resistor together with the charging of the trigger capacitor. In order to guarantee a precise and constant number of revolutions despite the longer duration of the ignition spark, connecting a Zener diode in blocking direction to earth in parallel to the trigger capacitor is planned whose Zener voltage drops out at the potentiometer-type resistor. As a result, the capacitor voltage is limited to the voltage of the Zener diode to approximately 120 Volts. The trigger capacitor, the Zener diode and the potentiometer-type resistor are connected in parallel in the known ignition circuit. The decisive factor in the situation of the maximum admissible revolution is the ON period activated by the trigger capacitor at the control input of the ignition thyristor. Its end is determined by the size of the trigger capacitor and the resistances of the potentiometer-type resistors, as well as by the sensitivity of the control input of the ignition thyristor and the amplitude of the alternating current which charges the trigger capacitor. The use of a sole parallel Zener diode in accordance with the known suggestion does not produce a sufficient avoidance of time fluctuations in the revolution limit. For example, with the ignition thyristor, the input lines which set the sensitivity differ from version to version. In the revolutions limiter circuit according to the design, the gate control current typically fluctuates between, for example, 200 nA and 1 xcexcA. A control threshold voltage of, for example, 700 mV can fluctuate by xc2x1150 mV, which in turn affects the current sensitivity in the circuit of the control input of the ignition thyristor. The sensitivity of the ignition thyristor is defined by the gate control current at which the thyristor switches through. The control threshold voltage does not change the sensitivity of the thyristor (based on its control current) but it does influence the gate control current in the circuit. In order to keep these effects as small as possible, the resistances of the potentiometer-type resistors are optimised according to the known suggestions and operate the revolution limitation with a relatively high control energy. Generally, typical values for the trigger capacitor are 220 nF, with the charge voltage being between 100 and 150V. In the discussed publication DE 196 45 466 A1, the charge voltage of the trigger capacitor is given as 120V.
The invention is based on the task of reducing the tolerances and inaccuracies in limiting the revolutions which are caused by the parts used in the revolutions limiting module and also the control energy required for the ignition circuit. In particular, the dynamics of the revolution-limiting module should be increased considerably if the working point is within the deviating control area of the ignition circuit.
As a solution, it is proposed, for the arrangement with the features discussed at the start, that a series Zener diode, which is operated in the blocking direction, be connected to the ignition circuit or its control input from the trigger charger element when it discharges a control current. The proposal differs from the statement in the patent publication mentioned above, DE 196 45 466 A1, because the control input of the ignition thyristor, according to the latter, is activated by a trigger capacitor via a potentiometer-type resistorxe2x80x94without the serial circuit for a Zener diode.
To increase the accuracy of the revolutions limiter further and, in particular, to compensate for unavoidable fluctuations in the available series Zener diodes, especially within their Zener breakdown voltages, after developing the invention, it is planned that a similar parallel Zener diode in the blocking direction be connected against the trigger charger element such that the charge voltage from the trigger charger element, especially for the trigger capacitor, is limited to the sum of the Zener breakdown voltages of the two Zener diodes. Preferably, the two Zener diodes will come from the same manufacturer so that they have the same electrical characteristics and control characteristics. As a result, their fluctuations can compensate each other. The Zener breakdown voltages for the two Zener diodes in the invention so designed that when the maximum admissible revolution is reached or the revolution limiter module is activated, both Zener diodes conduct at times while the trigger charger element is charging.
Based on the introduction of the series Zener diodes in the invention, the ignition circuit can be activated without further ado if, for the appropriate revolution, the alternating current conducted to the trigger charger element is so high that at least the series Zener diode can be transferred into breakdown. In order to increase the ignition reliability of the motor when starting, the development of the invention allowed for the revolution limiter module with the series Zener diodes to bridge a parallel current path from the alternating current to the control input of the ignition circuit. In other words, a further current path is planned from a resistance of the trigger source to the control input of the ignition circuit. The size of the parts of this current path determines the revolution with which ignition device on the motor switches on. The control impulses with limited duration from this current path to the control input of the ignition circuit are also useful as control impulses from the revolution limiter module. Thus the ignition circuit always receives a control impulse first from the named, bridged current path and then determines the ignition point of the ignition arrangement. With the appropriate development of the invention, this causes the bridging parallel current path to be realised with the resistance which, compared to the revolution limiter module formed with the charger, causes practically no dead time or run delay from the alternating current or trigger source.
Preferably, the ignition circuit is realised with a thyristor by which the control current at the control input required for switch through falls corresponding to the increasing voltage and increasing acceleration of this voltage at the anode-cathode paths. This can have negative effects for revolution just below the maximum admissible because it his area, the voltage at the ignition charger element or capacitor, which is connected to the switch path of the thyristor ignition circuit, increases particularly steeply. At the same time, the current at the control input of the thyristor has not yet returned to zero and can even be just below the threshold required for switch through. Because of the lowered threshold for the gate control current required for switch through of the thyristor ignition circuit, this ignition circuit can switch through unnecessarily during the charge phase of the ignition charger element. To prevent this, the invention is designed such that activation of the thyristor ignition circuit is stopped by the revolution limiter module using an additional block switch. This starts shortly after the start of the ignition charger charge phase until its end. To do this, a threshold switch can be used, for example, which switches through above a specific threshold for a control voltage. An advantageous development has the switch on threshold of the block switch designed such that the discharge of the ignition charger element or capacitor with the stated charge or voltage value above the ignition transfer does not cause a spark transfer to the spark gap.
As part of the general invention, there is also an independent use of the revolution limiter module on the invention as a revolution threshold regulator and/or toggle switch for universal use in connection with setting the revolution.
Further more, the general idea covers the following:
Arrangement to start a motor, especially in hand-held tools, with a magnetic generator (P;N;S) which induces alternating current based on the revolution and thus charges an ignition charger element (U4) for ignition energy, and with a trigger (U2, U10) which scans the alternating current (I, II, III) to activate an ignition circuit (U9) that is discharged via the primary coil of an ignition transfer (U5), where a revolution-related function is activated by a revolution circuit, which is designed such that the revolution circuit which works by comparing 2 fixed events with the time of an electronic circuit controlled by the RC timer, where the timer is started by a first fixed event (voltage pulse) and the switch state of the revolution circuit when the second event occurs is determined by the time of the second event (voltage pulse) relative to the controlling end of the timer, where the start of the control with the first fixed event and the end of the control with the charge amplitude being undercut by approximately 50% from C of the RC timer.
As a result, the ignition module has an application where the affected electrical circuit emits an impulse at the start of the second fixed voltage impulse when a certain revolution speed is exceeded. This circuit can be used in an ignition module where the ignition thyristor is controlled by the second fixed signal above a specific revolution speed. This signal still comes before the signal which controls the thyristor to discharge the ignition capacitor. This provides the function that carries out a jump xe2x80x9cearlyxe2x80x9d when a certain revolution is exceeded. The advantage of the circuit with the two Zener diodes also has an effect when the electrical circuit is a transistor, for example, since the amplification of a transistor also fluctuates in the same way as the thyristor gate trigger current and the threshold voltage on the control path of the transistor fluctuates comparably.
The invention is generally usable for revolution metering and not only for revolution limiting.
Example: adjustable jump:
Revolution metering by comparing two fixed events with the time of a timer corresponding to the invention, i.e. from the discharge curve of an RC unit, the flat part, preferably 50%, is divided by a series Zener diode ZDs so that only the steep part leads to the activation of an electronic circuit as above, where the series Zener diode ZDs together with a ZDp connected in this range determines the charge voltage of the capacitor of the RC unit.
Arrangements about how to start a motor, in particular, in hand-held machines, especially with a revolution threshold regulator and/or toggle switch with a magnetic generator which induces alternating current dependent on the revolutions and thus charges an ignition charger element for ignition spark energy, and with a trigger which scans the alternating current in order to activate a discharged ignition circuit in the ignition element in conjunction with the primary coil of an ignition transfer in the ignition charger element, with the trigger being a module for limiting the revolution speed of the motor and this revolution limiter working with a trigger charger element which can be recharged from a source of alternating current in the magnetic generator, which can be discharged by at least one path for controlling and activating the ignition circuit, where the trigger charger element, as it discharges, sends a control current to an ignition circuit via a series Zener diode in blocking direction and revolution threshold regulator and/or toggle switch, with an initial source of alternating current and a second source with fixed phase, which are both generated and which depend on and in their frequency in proportion to the revolution of a mutual rotor, and with a trigger which scans the alternating current in order to issue a control signal above or below the preset revolution threshold, where the trigger has a timer module, in particular RC-timer or monoflop, and this timer module works with a trigger which is charged from a source of alternating current which can be discharged by at least one path to create the control signal, where the trigger charger element, as it discharges, sends a control current to an ignition circuit via a series Zener diode in block direction.